In recent years, for example, a smartphone or a tablet terminal may include a touch panel, thereby allowing, for example, page-turning, zooming-in, or zooming-out of an image displayed on a screen to be performed by an intuitive pointing operation. On the other hand, as a display unit that performs display by projecting an image onto a screen, a projector (a projection display unit) has been long known. There is proposed a technique to add a detection function such as that of a touch panel to the projector, for example, as disclosed in PTLs 1 and 2.